1. Field of the Invention
This invention relates to disk drive suspensions, and more particularly, to a disk drive suspension and wireless electrical interconnects and flexures for a suspension. The interconnects have multiply variable shapes, thicknesses, widths, volumes and patterns in local portions of the trace conductors and the insulative layer over their lengths and widths to vary capacitance and thus impedance values in the circuits composed of the traces. The invention localized variations in the trace and insulative layer portions of a wireless suspension interconnect enables the suspension designer to accommodate design requirements for different impedances over the length or width of the electrical interconnect and to overcome the undesirable electrical effects of unavoidable features in the suspension such as tooling holes, all to make circuit impedance values smoother and more predictable, and therefore, signals more reliable at higher data rates.
2. Description of the Related Art
Typically a wireless disk drive suspension comprises a laminate of an insulative layer such as a plastic film and a plurality of trace conductors, usually copper or copper alloy that together form an electrical interconnect. The laminate may further comprise a metal layer that supports the assembly of the trace conductors and the insulative layer. In some cases a separate metal load beam comprised of one or more parts is used to support the assembly or the assembly plus the added metal layer. The load beam, usually of stainless steel, typically has a base section that attaches to an actuator, such as an actuator arm, a spring section and a rigid section that combine to exert a force called a gram load on a read-write head within a slider carried by the rigid portion at a disk. The suspension also typically includes a flexure supported on the load beam that may comprise metal or a laminate of a support metal such as stainless steel with a plastic film. The flexure may extend substantially the full length of the load beam rigid section and support one or more circuits comprising pairs or sets of the trace conductors that connect the read or write heads of the slider to the suspension electronics, e.g. at the base of the load beam. Construction of the flexure laminate is either additive in the sense that the several layers of metal, insulative film and trace conductors are built up on one another, or subtractive in the sense that a full laminate is reduced in one or more areas to fewer than all layers.
In either case the insulative layer between the metal layer, (or between the load beam if there is no laminate metal layer), and the trace conductors has been of the same thickness under the read trace conductors as under the write trace conductors and for the longitudinal and lateral extents of these trace conductors. As set forth hereinafter there are disadvantages to the same thickness of insulative layer at the read circuit conductors as at the write circuit conductors, especially in blocking achievement of a different impedance for these circuits.
The problem of achieving different impedances for read and write circuits is addressed in my copending parent applications above. A further problem of impedance control exists, however, occasioned by the irregular nature of the suspension structures, design requirements related to geometry of the traces, and other causes that effect an unintended and undesired variation in impedance and a consequent unwanted degradation in signal integrity.